Industrial control module providing universal I/O

ABSTRACT

An industrial control I/O module for interfacing with industrial control equipment, such as sensors and actuators, can be configured to dynamically provide differing resistances in each channel as may be required for reliably achieving particular modes of operation in the channel. Providing differing resistances in such channels flexibly allows different modes in the channel to provide universal I/O capability. Modes of operation could include, for example, digital output, digital input, analog output, analog input and the like, in the same channel, but at different times. In one aspect, a processor or voltage divider can be used to control an amplifier, with feedback, driving a transistor in a channel to dynamically adjust resistance in the channel by selectively biasing the transistor to achieve a resistance in the channel suitable for the selected mode.

FIELD OF THE INVENTION

The present invention relates to the field of industrial automation, andmore particularly, to a module for interfacing with industrial controlequipment through one or more universal I/O channels in whichresistances in such channels can be adjusted for various modes, such asmodes for digital output, digital input, analog output, analog input andanalog input with HART communications.

BACKGROUND OF THE INVENTION

Industrial controllers are specialized computer systems used for thecontrol of industrial processes or machinery, for example, in a factoryenvironment. Generally, an industrial controller executes a storedcontrol program that reads inputs from a variety of sensors associatedwith the controlled process and machine and, sensing the conditions ofthe process or machine and based on those inputs and a stored controlprogram, calculates a set of outputs used to control actuatorscontrolling the process or machine.

Industrial controllers differ from conventional computers in a number ofways. Physically, they are constructed to be substantially more robustagainst shock and damage and to better resist external contaminants andextreme environmental conditions than conventional computers. Theprocessors and operating systems are optimized for real-time control andare programmed with languages designed to permit rapid development ofcontrol programs tailored to a constantly varying set of machine controlor process control applications.

Generally, the controllers have a highly modular architecture, forexample, that allows different numbers and types of input and outputmodules to be used to connect the controller to the process or machineryto be controlled. This modularity is facilitated through the use ofspecial “control networks” suitable for highly reliable and availablereal-time communication. Such control networks (for example, ControlNetor EtherNet/IP) differ from standard communication networks (such asEthernet) by guaranteeing maximum communication delays by pre-schedulingthe communication capacity of the network, and/or providing redundantcommunication capabilities for high-availability.

As part of their enhanced modularity, industrial controllers may employI/O modules or devices dedicated to a particular type of electricalsignal and function, for example, detecting input AC or DC signals orcontrolling output AC or DC signals. Each of these I/O modules ordevices may have a connector system allowing them to be installed indifferent combinations in a housing or rack along with other selectedI/O modules or devices to match the demands of the particularapplication. Multiple or individual I/O modules or devices may belocated at convenient control points near the controlled process ormachine to communicate with a central industrial controller via thecontrol network.

Before commissioning I/O modules in the system, it is typicallynecessary to determine the I/O requirements at various points of thecontrolled process or machine to properly match channels of the I/Omodules to such requirements. For example, for analog sensors in acontrolled process, such as level sensors for tanks, temperature sensorsor position sensors, I/O modules having analog input channels should beused. However, for digitally controlled actuators in the controlledprocess, such as relays, indicator lights or small motors, I/O moduleshaving digital output channels should be used.

As a result, resources are typically required for allocating andcorrectly matching channels of I/O modules to corresponding industrialcontrol equipment. This requires time to implement, complexity to match,and limits flexibility of the system, particularly in the event that thecontrolled process or machine changes at a later date. Moreover, endusers must typically purchase, maintain and store many different I/Omodules to address each possible I/O type. If the required function ofan I/O point changes due to a change in the, end users application, theI/O module often needs to be replaced causing inconvenience, additionalcost and delay. It is therefore desirable to provide an I/O module forinterfacing with industrial control equipment which eliminates one ormore of the foregoing disadvantages.

SUMMARY OF THE INVENTION

An industrial control I/O module for interfacing with industrial controlequipment, such as sensors and actuators, can be configured todynamically provide differing resistances in each channel as may berequired for reliably achieving particular modes of operation in thechannel. Providing differing resistances in such channels flexiblyallows different modes in the channel to provide universal I/Ocapability. Modes of operation could include, for example, digitaloutput, digital input, analog output, analog input and the like, in thesame channel, but at different times. In one aspect, a processor orvoltage divider can be used to control an amplifier, with feedback,driving a transistor in a channel to dynamically adjust resistance inthe channel by selectively biasing the transistor to achieve aresistance in the channel suitable for the selected mode.

Accordingly, the invention can provide a universal I/O channelconfigurable to support multiple different I/O types, such as: digitalinput; digital output; analog input; analog output; Highway AddressableRemote Transducer (HART) communications, a digital industrial automationprotocol which can communicate over legacy 4-20 mA analoginstrumentation wiring; User Association of Automation Technology inProcess Industries (NAMUR), as described in DIN 19 234; and so forth.The universal I/O channel can provide a specific resistance to beestablished in the input or output channel for proper operation for eachof these I/O types. Moreover, the invention can advantageously providean I/O channel that can support currently defined, known I/O types, aswell as yet to be defined, future I/O types, providing universalflexibility.

In one aspect, a circuit can be configured to allow I/O channelresistance to be dynamically changed (programmed) based on the I/O typebeing supported by the channel. The circuit can use the I/O channelcurrent as well as the voltage to maintain the desired channelresistance. This resistance can be changed dynamically at any time asneeded. The circuit can allow the universal I/O channel to support, forexample, International Electrotechnical Commission (IEC) type 1, 2, 3inputs, as well as NAMUR. Also, when in analog input mode, the circuitcan configure a 250Ω input resistance optimal for HART communication.

In one aspect, a Field Effect Transistor (FET) in the channel canprovide infinitely configurable channel resistances. A processor orother logic controller can be used to read I/O current and voltagelevels. Resistances can be configured by processor (to adjustdigital-to-analog converter (DAC) output) based on Ohm's law,Resistance=Voltage/Current. In another aspect, resistance of the channelcan be adjusted by changing resistor values, including by configuring adigital potentiometer.

Such a circuit can allow any required channel resistance to beconfigured without the need of a physical resistor to be placed on aboard for each value. Accordingly, existing as well as new input and/oroutput types can be supported without hardware changes. Also, such acircuit can allow many different I/O types to be supported by singlechannel, such as IEC type 1, 2, 3 inputs, NAMUR, analog input with HARTcommunication, and so forth. Moreover, such a circuit could require lessprinted circuit board (PCB) space, thereby allowing higher channelcounts. Power dissipation can also be determined and activelycontrolled. In one aspect, the circuit can be configured to protectitself by limiting the maximum current allowed to flow. Such operationcan be accomplished actively with a processor or other control logic, orpassively with the one or more discrete elements, such as a currentsensing resistor.

Specifically then, one aspect of the present invention can provide amodule for interfacing with industrial control equipment, including: aterminal configured to receive an electrical conductor in a channelinterfacing with industrial control equipment; a variable resistancedevice connected to the terminal providing a resistance in the channel;and a control circuit connected to the variable resistance device. Thecontrol circuit can be configured to control the variable resistancedevice to adjust the resistance in the channel for a given mode selectedfrom multiple modes. Each mode can configure a different resistance inthe channel.

Another aspect of the present invention can provide an industrialcontrol system including: an industrial controller executing a controlprogram for controlling an industrial process; an I/O module incommunication with the industrial controller, the I/O module providing adirect interface to industrial control equipment of the industrialprocess, the I/O module including: a terminal configured to receive anelectrical conductor in a channel interfacing with the industrialcontrol equipment; a variable resistance device connected to theterminal providing a resistance in the channel; and a control circuitconnected to the variable resistance device. The control circuit can beconfigured to control the variable resistance device to adjust theresistance in the channel for a given mode selected from multiple modes.Each mode can configure a different resistance in the channel.

These and other objects, advantages and aspects of the invention willbecome apparent from the following description. The particular objectsand advantages described herein can apply to only some embodimentsfalling within the claims and thus do not define the scope of theinvention. In the description, reference is made to the accompanyingdrawings which form a part hereof, and in which there is shown apreferred embodiment of the invention. Such embodiment does notnecessarily represent the full scope of the invention and reference ismade, therefore, to the claims herein for interpreting the scope of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred exemplary embodiments of the invention are illustrated in theaccompanying drawings in which like reference numerals represent likeparts throughout, and in which:

FIG. 1 is a simplified diagram of an exemplar industrial control systemimplementing I/O modules interfacing with industrial control equipmentin accordance with an aspect of the invention;

FIG. 2 is a schematic of a circuit portion of an I/O module forinterfacing with industrial control equipment in the system of FIG. 1 inaccordance with an aspect of the invention; and

FIG. 3 is a schematic of an alternative circuit portion of an I/O modulefor interfacing with industrial control equipment in the system of FIG.1 in which a resistor divider is used in accordance with aspect of theinvention.

DETAILED DESCRIPTION OF THE OF THE INVENTION

Referring now to FIG. 1, an exemplar industrial control system 10suitable for application of the present invention may provide one ormore industrial controllers 12 a, 12 b, which could be programmablelogic controllers (PLC's), operating to execute a control program forthe control of an industrial process 14 as is generally understood inthe art. The industrial process, for example, may coordinate a set ofmachines on an assembly line or the like, or interact with actuators,sensors and/or other industrial control equipment of plant processingmaterials to control that process, or conduct other similar controlapplications.

The industrial controllers 12 can communicate downstream with one ormore control I/O modules 16 a-16 c providing a direct interface toindustrial control equipment 20 of the industrial process 14. Such I/Omodules 16 provide input and output lines via electrical conductors 18to and from the industrial process 14 allowing communication with theindustrial control equipment 20, such as equipment 20 a-20 d. Theindustrial control equipment 20 could include, for example: digitalactuators, such as relays, indicator lights or small motors; digitalsensors, such as photoelectric sensors, dry contact sensors, inductivesensors or push buttons; analog actuators, such as valves, positionersor meters; analog sensors, such as level sensors for tanks, temperaturesensors or position sensors; and/or HART compatible devices.

The industrial controllers 12 can communicate with the control I/Omodules 16 through an industrial control network 24, such as CommonIndustrial Protocol (CIP), EtherNet/IP, DeviceNet, CompoNet orControlNet network, whose specifications are published and whoseprotocols are used broadly by a number of manufacturers and suppliers.Such networks provide for high reliability transmission of data in realtime and can provide features ensuring timely delivery, for example, bypre-scheduling communication resources such as network bandwidth,network buffers, and the like.

The industrial controller 12 can also communicate upstream, through adata network 26 (which may, but need not be an industrial controlnetwork) via one or more routers or switches 28, with a central computersystem 30. This latter computer system 30 may further communicate viathe Internet 32 with remote devices 34 such as computer terminals,mobile wireless devices, and the like. Alternatively, there may be adirect connection between the industrial controller 12 and the Internet32.

As is generally understood in the art, each of the I/O modules 16,industrial controllers 12, switches 28, computer system 30 and remotedevices 34 may provide one or more electronic processors and associatedelectronic memory holding programs executable by the processors, some ofwhich are described below.

Referring now to FIG. 2, a schematic of a circuit portion 17 of an I/Omodule 16 for interfacing with industrial control equipment 20 in auniversal I/O channel is provided in accordance with an aspect of theinvention. In the circuit portion 17, the I/O module 16 can includemultiple terminals 40, such as terminals T1, T2, T3, each beingconfigured to receive electrical conductors, such as conductors 18 a, 18b, 18 c, respectively, in channels interfacing with the equipment 20.The conductors 18 a, 18 b, 18 c are illustrated in phantom linesindicating the various possibilities for connection to the equipment 20according to various devices and/or modes. Accordingly, the conductors18 can be wires variously configured for communicating with equipment20, which could comprise sensors or actuators, any of which may bedigital, analog and/or HART devices, as may be desired at various pointsin the industrial process 14. Such conductors 18 can be releasablyconnected to the I/O module 16 at the terminals 40. In one aspect, theterminals 40 can be screw terminals in which a screw driver, such as aslotted or flat-blade screwdriver or other type, can be used toreleasably connect the conductors 18 to the I/O module 16.

A variable resistance device 42, which can be a transistor, and whichpreferably can be a Field Effect Transistor (FET), can be connected to aterminal 40, such as the terminal T2, providing a resistance in thechannel (identified as “B”) in line with the conductor 18 b. A controlcircuit, which in one aspect can include a processor 44 connected to anamplifier 46, can be connected to the variable resistance device 42. Thecontrol circuit can be configured to control the variable resistancedevice 42 to adjust the resistance in the channel in line with theconductor 18 b for a given mode selected from multiple modes ofoperation. A mode of operation can be determined, such as by theprocessor 44, from user input which could indicate requirements for theequipment 20, which could be provided through a screen of a remotedevice 34, the central computer system 30 or the industrial controller12 or to the I/O module 16 directly. Such user input may indicate, forexample, power, voltage and/or current requirements for the equipment20, or simply whether the equipment 20 is a predetermined device type,such as a digital sensor, including an IEC type 1, 2, 3 or NAMUR sensor,a digital actuator, an analog sensor, an analog sensor operating as aHART device, or an analog actuator, or a user defined device type.Determined modes of operation could then be set, such as digital output,digital input for IEC type 1, 2, 3 or NAMUR, analog output, analog inputwithout HART communications, analog input with HART communications(which can be implemented in a 4-20 mA current loop), user defined, andso forth. Accordingly, each mode of operation could configure adifferent resistance in the channel specific for the device type.

For example, a mode for digital output could cause the control circuitto control the variable resistance device to minimize the resistance inthe channel, preferably to 0Ω; a mode for digital input for IEC type 1,2, 3 could cause the control circuit to control the variable resistancedevice to adjust the resistance in the channel to a higher resistance(than for analog input), such as to 3.3 k Ω; a mode for digital inputfor NAMUR could also cause the control circuit to control the variableresistance device to adjust the resistance in the channel to a higherresistance (than for analog input), but with less resistance than forIEC type 1, 2, 3, such as to 1 k Ω; a mode for analog output could causethe control circuit to control the variable resistance device to varythe resistance in the channel to maintain a constant current in thechannel; a mode for analog input with HART communications could causethe control circuit to control the variable resistance device to adjustthe resistance in the channel to a lower resistance (than for digitalinput), such as to 250Ω; and a mode for analog input without HARTcommunications could also cause the control circuit to control thevariable resistance device to adjust the resistance in the channel to alower resistance (than for digital input), but even less resistance thanfor an analog input with HART communications, such as to 100Ω. Loweringthe resistance in the channel even further, from 250Ω to 100Ω, for ananalog input without HART communications, for example, canadvantageously provide power savings in the system without requiring asingle resistance for both types.

The control circuit can control the variable resistance device 42 toprovide the resistance in the channel (B) as desired by receivingfeedback from the channel for the amplifier 46 which, in turn, canprovide the adjustment for the variable resistance device 42, such as bydriving a gate of the FET to selectively bias the transistor to achievea resistance in the channel suitable for the selected mode. In oneaspect, a voltage feedback line 50 (“V_IN”), from a node between thevariable resistance device 42 and the screw terminal T2, and a currentfeedback line 52 (“I_IN”), from a node between the variable resistancedevice 42 and a current sensing resistor 54, can be connected to theprocessor 44. The current sensing resistor 54 could be a nominalresistor, such as 20Ω, connected to ground. The processor 44, in turn,can calculate a resistance for the channel based on Ohm's law,Resistance=Voltage/Current, in this case, dividing voltage from thevoltage feedback line 50 by current from the current feedback line 52.Based on the mode desired, the processor 44 can then execute to adjustthe resistance in the channel by adjusting a digital-to-analog converter(DAC) output 56 (“ADJ”) to an input of the amplifier 46, such as aninverting input (“−”), so that the amplifier 46, in turn, provides theadjustment to the variable resistance device 42 through a biasing line58. The current feedback line 52 can also be provided to another inputof the amplifier 46, such as a non-inverting input (“+”), providing areference. The amplifier 46 could be, for example, an ADA 4891 Low CostCMOS, High Speed, Rail-to-Rail Amplifier, as available from AnalogDevices, Inc. of Norwood, Mass.

Referring briefly to FIG. 3, where like reference numerals representlike parts throughout, in an alternative aspect, an alternative circuitportion 17′ illustrates an alternative control circuit for the I/Omodule 16. In the alternative control circuit, a resistor divider 60 canbe connected to the amplifier 46. In this aspect, the voltage feedbackline 50, from the node between the variable resistance device 42 and thescrew terminal T2, can be connected to a first side of a first resistor62 in the resistor divider 60. A second side of the first resistor 62,at an adjusting node 66, can be connected in series to a first side of asecond resistor 64 in the resistor divider 60. The second side of thesecond resistor 64 can be connected to ground. The second resistor 64could be, for example, a digital potentiometer which could be configuredby a processor to implement various resistances. The adjusting node 66,in turn, can then adjust the resistance in the channel by adjustinginput of the amplifier 46, such as the non-inverting input (“+”), sothat the amplifier 46, in turn, provides the adjustment to the variableresistance device 42 through the biasing line 58. The current feedbackline 52 can again be provided to another input of the amplifier 46, suchas the inverting input (“−”), providing a reference. Accordingly, theprocessor, which could determine a given mode from user input, canconfigure the second resistor 64 (digital potentiometer) according tothe given mode to implement the desired resistance in the channel.

Referring again to FIG. 2, various modes of operation which can beimplemented by the I/O module 16, using the circuit portion 17 or thealternative circuit portion 17′, include, for example: digital output,digital input for IEC type 1, 2, 3 or NAMUR, analog output, analog inputwithout HART communications, analog input with HART communications(which can be implemented in a 4-20 mA current loop). Moreover, afurther customized, user defined mode of operation can also be provided.

By way of example, in a first mode for digital output, such as forequipment 20 comprising digital actuators such as indicator lights orsmall motors, the processor 44 can control a switch 70 to selectivelyprovide power from a power source 72 to terminal T1 in an output channel(identified as “A”) as required by the digital device. A conductor 18 a,releasably connected to the terminal T1, can provide such selectivelydelivered power to the equipment 20. A conductor 18 b, releasablyconnected to the terminal T2, in turn, can provide a return path in areturn channel (channel B), in line with the variable resistance device42, from the equipment 20. In the return path (channel B), the controlcircuit (using processor 44 and/or resistor divider 60) can control thevariable resistance device 42 to minimize the resistance in the channel,such as by biasing the FET to 0Ω, as may be required by the system.

In a second mode for IEC digital input, such as for equipment 20comprising IEC type 1, 2, 3 digital sensors, such as photoelectricsensors, dry contact sensors, inductive sensors or push buttons, aconductor 18 b, releasably connected to the terminal T2, can provide aninput from the equipment 20. A conductor 18 c, releasably connected tothe terminal T3, can provide a return path in a return channel (channelC) connected to ground. In the input path (channel B), the controlcircuit (using processor 44 and/or resistor divider 60) can control thevariable resistance device 42 to adjust the resistance in the channel toa higher resistance (than for analog input), such as to 3.3Ω, as may berequired by the system.

In a third mode for NAMUR digital input, such as for equipment 20comprising NAMUR sensors, a conductor 18 b, releasably connected to theterminal T2, can again provide an input from the equipment 20. Aconductor 18 c, releasably connected to the terminal T3, can againprovide a return path in a return channel (channel C) connected toground. In the input path (channel B), the control circuit (usingprocessor 44 and/or resistor divider 60) can control the variableresistance device 42 to adjust the resistance in the channel to a higherresistance (than for analog input), but with less resistance than forIEC type 1, 2, 3, such as to 1 k Ω.

In a fourth mode for analog output, such as for equipment 20 comprisinganalog actuators such as such as valves, positioners or meters, theprocessor 44 can control a switch 70 to selectively provide power from apower source 72 to terminal T1 in an output channel (identified as “A”)as required by the analog device. A conductor 18 a, releasably connectedto the terminal T1, can provide such selectively delivered power to theequipment 20. A conductor 18 b, releasably connected to the terminal T2,in turn, can provide a return path in a return channel (channel B), inline with the variable resistance device 42, from the equipment 20. Inthe return path (channel B), the control circuit (using processor 44and/or resistor divider 60) can control the variable resistance device42 to vary the resistance in the channel to maintain a constant currentin the channel.

In a fifth mode for analog input with HART communications, such as forequipment 20 comprising HART compatible devices, a conductor 18 b,releasably connected to the terminal T2, can provide an input from theequipment 20 to a HART modem 80. A conductor 18 c, releasably connectedto the terminal T3, can provide a return path in a return channel(channel C) connected to ground. In the input path (channel B), thecontrol circuit (using processor 44 and/or resistor divider 60) cancontrol the variable resistance device 42 to adjust the resistance inthe channel to a lower resistance (than for digital input), such as to250Ω.

In a sixth mode for analog input without HART communications, such asfor equipment 20 comprising level sensors for tanks, temperature sensorsor position sensors, a conductor 18 b, releasably connected to theterminal T2, can again provide an input from the equipment 20. Aconductor 18 c, releasably connected to the terminal T3, can provide areturn path in a return channel (channel C) connected to ground. In theinput path (channel B), the control circuit (using processor 44 and/orresistor divider 60) can control the variable resistance device 42 toadjust the resistance in the channel to a lower resistance (than fordigital input), but even less resistance than for an analog input withHART communications, such as to 100Ω. Lowering the resistance in thechannel even further, from 250Ω to 100Ω, for an analog input withoutHART communications, for example, can advantageously provide powersavings in the system without requiring a single resistance for bothtypes. Additional user defined modes can be further configured,including for supporting future I/O types with existing hardware.

Certain terminology is used herein for purposes of reference only, andthus is not intended to be limiting. For example, terms such as “upper,”“lower,” “above,” and “below” refer to directions in the drawings towhich reference is made. Terms such as “front,” “back,” “rear,”“bottom,” “side,” “left” and “right” describe the orientation ofportions of the component within a consistent but arbitrary frame ofreference which is made clear by reference to the text and theassociated drawings describing the component under discussion. Suchterminology may include the words specifically mentioned above,derivatives thereof, and words of similar import. Similarly, the terms“first,” “second” and other such numerical terms referring to structuresdo not imply a sequence or order unless clearly indicated by thecontext.

When introducing elements or features of the present disclosure and theexemplary embodiments, the articles “a,” “an,” “the” and “said” areintended to mean that there are one or more of such elements orfeatures. The terms “comprising,” “including” and “having” are intendedto be inclusive and mean that there may be additional elements orfeatures other than those specifically noted. It is further to beunderstood that the method steps, processes, and operations describedherein are not to be construed as necessarily requiring theirperformance in the particular order discussed or illustrated, unlessspecifically identified as an order of performance. It is also to beunderstood that additional or alternative steps may be employed.

It is specifically intended that the present invention not be limited tothe embodiments and illustrations contained herein and the claims shouldbe understood to include modified forms of those embodiments includingportions of the embodiments and combinations of elements of differentembodiments as coming within the scope of the following claims. All ofthe publications described herein including patents and non-patentpublications are hereby incorporated herein by reference in theirentireties.

What is claimed is:
 1. A module for interfacing with industrial controlequipment, comprising: a terminal configured to receive an electricalconductor in a channel interfacing with industrial control equipment; avariable resistance device connected to the terminal providing aresistance in the channel; and a control circuit connected to thevariable resistance device, wherein the control circuit is configured tocontrol the variable resistance device to adjust the resistance in thechannel for a given mode selected from a plurality of modes, whereineach mode of the plurality of modes configures a different resistance inthe channel, and wherein the plurality of modes includes modes fordigital output, digital input, analog output and analog input.
 2. Themodule of claim 1, wherein the terminal is a screw terminal, and whereinthe variable resistance device is a transistor.
 3. The module of claim2, wherein the control circuit comprises a processor connected to anamplifier, wherein the transistor is a Field Effect Transistor (FET),and wherein the amplifier drives a gate of the FET.
 4. The module ofclaim 3, further comprising a resistor for current sensing connected tothe FET, wherein the resistor is further connected to a first input ofthe amplifier and the processor is connected to a second input of theamplifier.
 5. The module of claim 3, wherein the given mode isdetermined by the processor from user input.
 6. The module of claim 2,wherein the control circuit comprises a resistor divider connected to anamplifier, wherein the transistor is a Field Effect Transistor (FET),and wherein the amplifier drives a gate of the FET.
 7. The module ofclaim 6, wherein the resistor divider comprises a resistor in serieswith a digital potentiometer.
 8. The module of claim 7, furthercomprising a processor for configuring the digital potentiometer,wherein the given mode is determined by the processor from user input,and wherein the processor configures the digital potentiometer accordingto the given mode.
 9. The module of claim 1, wherein the control circuitcontrols the variable resistance device to provide a higher resistancein the channel when the mode is for digital input and a lower resistancein the channel when the mode is for analog input.
 10. The module ofclaim 1, wherein the plurality of modes further includes a mode foranalog input with Highway Addressable Remote Transducer (HART)communications in a 4-20 mA current loop.
 11. The module of claim 10,wherein the control circuit controls the variable resistance device toprovide a higher resistance in the channel when the mode is for analoginput and a lower resistance in the channel when the mode is for analoginput with HART communications.
 12. The module of claim 1, wherein thecontrol circuit controls the variable resistance device to minimize theresistance in the channel when the mode is for digital output.
 13. Themodule of claim 1, wherein the control circuit controls the variableresistance device to vary the resistance in the channel to maintain aconstant current in the channel when the mode is for analog output. 14.The module of claim 1, wherein the terminal is a first terminal in afirst channel, and further comprising a second terminal configured toreceive an electrical conductor in a second channel interfacing withindustrial control equipment comprising an actuator, and wherein thesecond channel provides an output from a power source to the industrialcontrol equipment in the modes for digital output and analog outputwhile the first channel provides a return path.
 15. The module of claim1, wherein the terminal is a first terminal in a first channel, andfurther comprising a second terminal configured to receive an electricalconductor in a second channel interfacing with industrial controlequipment comprising a sensor, and wherein the first channel provides aninput from the industrial control equipment in the modes for digitalinput and analog input while the second channel provides a return pathto ground.
 16. An industrial control system comprising: an industrialcontroller executing a control program for controlling an industrialprocess; an I/O module in communication with the industrial controller,the I/O module providing a direct interface to industrial controlequipment of the industrial process, the I/O module comprising: aterminal configured to receive an electrical conductor in a channelinterfacing with the industrial control equipment; a variable resistancedevice connected to the terminal providing a resistance in the channel;and a control circuit connected to the variable resistance device,wherein the control circuit is configured to control the variableresistance device to adjust the resistance in the channel for a givenmode selected from a plurality of modes, wherein each mode of theplurality of modes configures a different resistance in the channel,wherein the given mode is determined from user input, and wherein theplurality of modes includes modes for digital output, digital input,analog output and analog input.
 17. The industrial control system ofclaim 16, wherein the terminal is a screw terminal, and wherein thevariable resistance device is a FET with the control circuit connectedto a gate of the FET.
 18. The industrial control system of claim 16,wherein the plurality of modes further includes a mode for analog inputwith HART communications.
 19. The industrial control system of claim 18,wherein the control circuit controls the variable resistance device tominimize the resistance in the channel when the given mode is fordigital output, and wherein the control circuit controls the variableresistance device to vary the resistance in the channel to maintain aconstant current in the channel when the given mode is for analogoutput.